The vacuum countergravity, shell mold casting process is particularly useful in the making of thin-walled castings and involves: sealing a bottom-gated mold, having a gas-permeable upper portion, to the mouth of a vacuum chamber such that the chamber confronts the upper portion; immersing the underside of the mold in an underlying melt; and evacuating the chamber to draw melt up into the mold through one or more of the gates in the underside thereof. Such a process is shown in U.S. Pat. No. 4,340,108 wherein the mold comprises a resin-bonded-sand shell having an upper cope portion and a lower drag portion sealingly bonded together. U.S. Pat. No. 4,340,108 seals the mold to the vacuum chamber atop the cope such that the parting line between the mold halves lies outside the vacuum chamber. Copending U.S. patent application Ser. No. 654,404 filed Sept. 26, 1984 in the name of Roger Almond, and assigned to the assignee of the present invention, seals the mold to the vacuum chamber atop the drag such that the parting line between the cope and drag falls within the vacuum chamber. In such processes, and particularly that shown in Ser. No. 654,404, the gasket material used to seal the vacuum chamber to the mold is necessarily brought into close proximity to the surface of the underlying melt during casting. Hence the gasket material is exposed to the tremendous heat that radiates from the melt pot. As a result, only highly temperature resistant gasket materials, such as Fiberfrax, (from the Carborundum Co.) or the like, has been used, heretofore. In this regard, Fiberfrax strips are typically glued to the surface of the mold and the mouth of the vacuum chamber pressed firmly against the material to compress it and form the desired mold-chamber seal. When so applied and used extra time is required to manually affix the gaskets to each mold and the gasket material is ultimately destroyed with the mold following casting. It would be desirable if an elastomeric gasket material could be affixed to the mouth of vacuum chamber for repeated use with many molds. This would eliminate the time required to manually prepare each mold-chamber seal as well as the unnecessary consumption of gasket material. Unfortunately, elastomeric gasket materials cannot survive the kind of direct exposure to the radiant heat from the molten metal that the Fiberfrax seals have had to endure.
It is an object of the present invention to provide improved apparatus for the vacuum countergravity casting of shell molds wherein the vacuum chamber is sealed to the mold at a site which is substantially thermally insulated (i.e., conduction-wise) and shielded (i.e., radiation-wise) from the surface of the metal melt during casting so as to permit the repeated use of a thermally degradable elastomeric gasket at the site. This and other objects and advantages of the present invention will become more readily apparent from the detailed description thereof which follows.